Electrical  measuring instrument



March 16, 1948.

D. A. YOUNG ET AL ELECTRICAL MEASURING INSTRUMENT Filed sept. 2, 1945 4 Sheets-Sheet l oag/USS A. Young, Law/ence JL was @nde/Ward eme/mi2 ATTORNEY March 16, 194s. D, A YOUNG ET AL 2,438,027

ELECTRICAL MEASURING INSTRUMENT Filed Sept. 2, 1943 4 Sheets-Sheet 2 @j 127 ATTORNEY March 16, 194s. D.A.YUNG Em v2,438,027

ELECTRI CAL MEASURING INSTRUMENT Filed Sept. 2, 1943 4 Sheets-Sheet 5 l/ l\ l 155 lNvENToRs d@mfg/g55 A. Y0U/2g, Lawrence .I L mas ATTORN EY March 416, 194s.

D. A. YOUNG ET AL ELECTICAL 'MEASURING INSTRUMENT Filed Sept. 2, 1943 4 Sheets-Sheerl 4 INVENTORS f Bong/ass A. y0u/7 9, Law/ence Jamas Il. 24. H7107 efnarag .Le/767ml?.

ATTORNEY Patented Mar. 106, 1948 STATES. PArENT orties ELECTRICAL MEASURING I INSTRUMENT Douglass AI Young; East Orange, v Law-rence JQ? Lunas, Cedar Grove, and BernaifE. Len'ehan',V

Bloomfield; N; J.;

assign'orsi to Westinghouse Electric Corporation, East'Piltsbugh Pal.; acor.V` porationI of :Pennsylvanial Application- Scptember 2, 194.3.v Serial-No; 500,896

16 C13/img.' (Cl. 171-95) This invention relates to electromagnetic de`4 vices, and it has particular relation to long-scale' electrical measuring instruments suitable" for measuring a function of two variable electrical quantities.

Electromagnetic devices responsive toa func'- tion of a plurality of variable quantities are Awell known in the art. For example, reference'mayv be made to an electrodynamic measuring instru;

ment which is employed for measuring functions" of voltage and current such as watts, vars'and' power factor. in its most commonfoi'in, the electrodynamic instrument is an air core instru'- ment having a xed coil, and having a movable coil which is mounted for rotation with respect 't the xed coil. An indicating device, such as 'a pointer or pen, is attached to the movable coil for rotation through an arc which generallyis substantially less than 180.

In some cases, it is desirable to emploi7` a mag;

netic core for an electrodynamic instrument. This is particularly true of long-scale electrody'- namic instruments, wherein the'increased torque resulting from the utilization of a magnetic core is desirable.

250. By utilizing a magnetic core of suitable 'design it is possible to provide in a lon'g-scale'in-V strument a, long arcuate air gap having a satis# factory magnetic iiux distribution therein'.

Such long-scale instruments may be designed to rotate an indicator device such as? a pointer o-r pen with reference to a'scaleor chartr through an angle which may be of the orderv ol" The provision of a magnetic core in an. electrodynamic instrument has complicated materially the assembly and disassembly of the instrument. having two separate, single-phase elements or units designed to measure electrical quantities in' a three-wire or polyphase circuit. In apolyphase instrument of this type two separate single-phase' units are employed, the movable coils of which areV attached to a common shaft. When magnetic cores are pro-vided, suitable means and procedure must be developed for inserting the magnetic cores in their appropriate coils.

If the magnetic core for a movable coil is asyinmetric with respect to the path of travel of the` movable coil, the core and coil in eiect constitute an electromagnetic solenoid. through the coil produces a force urging the coil towards a position wherein the magnetic core olers its lowest magnetic reluctance to magnetic" Since this force,v if present in an electrodynamic measuring instruf iiuX produced hy the current.

ment, maybe a source oi errorit is desirablethat This is particularly true for instruments Current passing" 2 themagn'etlc core" be"syrrmetic` with-respect to the pathof 'travel ofthe coil.'

In accordance with`the"inven`tion;l a magnetic structure is provided" foran electromagnetic de'- vice orunit, such as'an electrodynam'ic measuring.,

instrument. This magnetic" structur, as' einployec'forav sihgle-ph'ase'instrumentorlunit, i171-4 cludes two Ia'giieticportions which are asy'mmetric Withrespectto the path' of travel of t'he movable vcoil; However; theasymmetris ofthe` two'magn'etic portions are so locatdwith' respect' to thepath'of'tl'vl ofthe/movable COil thatlth resultant magnetic Stll'ctul iS Substantially-Sym; metric withrespct 'to such path.' Y

In a.' preferred embodiment-f the ini/enticing.. the" magnetic" structure` iri-cli'ides'v two ann'i'llarV magnetic cores Seach having achannel extendir'lgl radallyfrrn the llt-I t0- th eXtell'lthebf'.

niovablecoil therethrough. These an'nulargmagfnetic cores Vare mounted inalignment 'on' the axis o-f rotation of the movable coil with'lth'eir channels disposed respectivelyl adiacentv the twoendsV of the path of travel vofthe movable'coil.vr Because `of this' angular spacing of the channels', thetwo annular magnetic cores provide a resultant magnetic "structure which -is .substantially 4`syinrn`etric With-'respect ttl'l'e pth" of ti'vel 'of'the nick/able? coil.

'I'he annular magnetic cores 'arespaced 'axially alogth'aXiS bf 'rotation' of th rotatable 'c by" adistanoe sufficient to permit"passage'pfa'side `Of-the coil'rthebtweel; Tlli's"pe'rntsI ito'du'- tion of one side of the coil through" one ofthe" "channels, rotation of 4the'coil to' a position' adjament A further problem is presented in tllerprovii" sion of `suitableconnectioris Vfor theI movable coils of a long-scale m'easuring"instrument.` 'Thisis particularly true of apolyphasameasuring"inl 'strumenti wherein four `'leads` from two movable coils must be connected to a compact terminal assembly. In accordance with a further aspect of the invention, a plurality of spacers in the form of collars are mounted on the coil shaft. These collars have intertting male and female parts and may be of similar construction. The male and female parts are so located that each collar is rotated angularly with respect to its adjacent collar about the axis of rotation of the shaft. A plurality of flexible conductor strips is provided, each of which is positioned by a separate one of the collars. Because of the angular and axial spacing of the collars each of the conductor strips is suitably axially and angularly positioned with respect to the axis of the shaft.

It is, therefore, an object of the invention to provide an improved electromagnetic device which is responsive to a function of two variable quantities.

It is a further object of the invention to provide an improved polyphase electrodynamic measuring instrument having a long scale.

It is a still further object oi the invention to eliminate substantially all solenoid action in an electrodynamic instrument having an asymmetric magnetic core element.

It is another object of the invention to provide an electrodynamic instrument having a rotatable coil provided with two asymmetric magnetic cores, with the asymmetries of the magnetic cores so disposed that the resultant magnetic core is substantially symmetric with respect to the path of travel of the coil.

It is an additional object oi the invention to provide an electrodynamic instrument having a rotatable coil and having a pair of annular magnetic cores each provided with a radial channel, the channels being disposed respectively adjacent the opposite ends of the path of travel of the coil to provide a resultant magnetic core which is substantially symmetric with respect to the path of travel of the coil.

It is a still further object of the invention to provide an improved terminal assembly for the rotatable coil assembly of an electrodynamic instrument.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a View in sectional elevation of a polyphase electrodynamic measuring instrument embodying the invention,

Fig. 2 is a view in top plan of the instrument illustrated in Fig. 1,

Fig, 3 is a view in front elevation with parts broken away, and parts rotated with respect to each other, of a rotor assembly suitable for the instrument of Fig. 1,

Fig. 4 is a view in perspective with parts broken away and parts exploded showing the relationship of parts of the instrument of Fig. 1,

Figs. 5 and 6 are views in top plan of laminations suitable for the magnetic structures employed in the instrument of Fig. 1,v

Figs. 7, 8 and 9 are views respectively in top plan, side elevation and bottom plan of a spacer or collar employed in the terminal assembly of an instrument,

Fig. 10 is a view in top plan of a conducting strip and a holder suitable for an instrument terminal assembly,

Fig. 11 is a view in side elevation of the conducting strip and holder of Fig. 10 with a portion bent into nal position,

Figs. 12 to 17, inclusive, are views taken re- 4 spectively on the lines XII-XII, XIII-XIII, XIV-XIV, XVXV, XVI-XVI and XVII-XVII of Fig. 3,

Figs. 18, 19, 20 and 21 are views taken respectively on the lines XVIII-XVIH, mX-XIX, XX-XX and XXI- XXI of Fig. 1,

Fig. 22 is a detail view in sectional elevation showing the attachment of the stator of Fig. 1 to a base member,

Fig. 23 is a view in sectional elevation of an instrument embodying a modiiied form of the invention, and

Fig. 24 is a diagram of circuit connections suitable for the instrument of Fig. 23.

Referring to the drawings, Fig. 1 shows an electro-dynamic measuring instrument suitable for measuring electrical quantities in a threewire or polyphase electrical circuit. This instrument includes a stator assembly I and a rotor or shaft assembly 3 which is mounted for rotation with respect to the stator assembly. The stator assembly comprises a pair of magnetic structures 5 and 'I which are securely bolted to a base member 9. The stator assembly also includes a bearing support I I having a ring-shaped supporting plate I3 which may be secured in position by the bolts employed for securing the stator assembly to the base member 9. The bearing support II includes an arm I5 having in threaded engagement therewith a bearing screw I'I which provides a lower bearing for the rotor assembly 3. The bearing support II also has secured thereto a bridge plate I9 in which a bearing screw 2I is threadedly positioned for completing the bearing support for rotor assembly 3. The bridge plate I9 is further supported by a pillar 23 secured to the plate I3, and may be secured to the bearing support I I and the pillar 23 in any suitable manner as by machine screws 25. y

For biasing the rotor assembly 3 to a predetermined position with respect to the stator assembly, a spiral control spring 21 is carried by the rotor assembly and has its outer end attached to a disk 29 rotatably mounted on a hollow rivet 3| which is secured to the bridge plate IS, Rotation of the disk 29 is effected through an adjacent disk 33 in biased, frictional engagement therewith by adjustment of a zero-adjuster lever 35 which is pivotally secured to the bridge plate I9 by means of a machine screw 31. The lever 35 determines the position of a pin 39 which, in turn, determines the position of the disk 33.

For indicating movements of the rotor assembly, the rotor assembly 3 has a pointer 4I which projects through an annular groove in the bridge plate I9 and overlies a dial plate 43. The dial plate is of a dished formation having an arcuate flange 45 adjacent the tip of the pointer 4 I Suitable scale markings may be applied to the flange 45, as shown more clearly in Fig. 2. An arcuate plate 41 having scale numerals thereon may be secured to the dial plate 43 in any suitable manner as by riveting. As shown in Fig, 2, the instrument is of the center-zero type, wherein the pointer 4I may be deflected in either of two directions away from the central point. As well understood in the art, the rotor assembly may be adjusted to provide an instrument wherein the pointer is normally at one end of the scale when the instrument is deenergized and is deflected towards the other end 0f the scale in response to energization of the instrument. Suiten'dsof the path of' travel of the pointer 4| to engage the pointer and prevent overtravel thereof.

The casing for the instrument of Fig. 1 may take the form of a magnetically soft steel cylindrical shell 139 which serves as a magnetic shield for the instrument. The shell 49 has an inwardly turned flange 5| which engages a flange 53 of the base member 9. A gasket 55 may be interposed between the flanges. The base member 9 may be formed of a suitable insulating material, such as a phenolic resin, and may carry terminal screws 5l which are connected to the windings of the instrument by means of conductors 59.

At its opposite end the shell a9 may have an outwardly'extending ange 5| for reception of a cap 63. The cap 53 may be formed of a suitable material, such as steel or a phenolic resin, and has a transparent window 65 associated therewith for exposing the pointer and dial assembly of the instrument. If desired, the cap andiiange 5| may have a rectangular outline as illustrated in Fig. 2. rI'he cap may be attached to the shell 99 by means of machine screws 6l. The instrument may be mounted in any suitable manner. For example the' shell d may pass through an opening in a panel P and may be secured to the panel by machine screws (not shown).

For actuating the zero adjustment of the instrument, a zero-adjuster button 59 is held captiveby the cap 53. This button has an eccentric pin 'll extending into an opening in the lever 35. Rotation of the button 59, therefore, serves to rotate the lever and thereby to adjust the control spring Zl'. The casing, zero-adjuster mechanism and dialassembly of the instrument illustrated in Figl may be similar to the corresponding structure disclosed in the copending application of V. S. Thomander, Serial No. 500, 895, filed September 2, 1943, now Patent 2,389,- 393, and assigned to the same assignee.

In instruments of the type herein described,

` it is desirable to damp movements of the rotor assembly. To this end, the rotor assembly includes a damping disk 'i3 which is formed of an electroconductive material such as aluminum or copper. The damping disk 'I3 is positioned for rotation in the magnetic field produced by a pair of U-shaped permanent magnets l5. These magnets are attached to a framework which includes a base plate 'il and a plate 19 which is formed of a magnetically-soft material, such as soft steel. The plates 'il and i9 are attached to each other by means of pillars Si and the entire framework is attached to the bridge plate i9 by means of screws (not shown). It will be noted that the poles of the magnets 'i5 are spaced from the magnetic plate 'i9 to define an air gap within which the damping disk 'i3 is mounted for rotation, The entire framework is so configured that it may be removed from the rotor assembly in a radial direction with respect to the axis of the rotor assembly. This construction is illustrated more particularly in Fig- 19.

As shown more clearly in Fig. 3, the rotor assembly 3 includes a shaft 83 having pivots 85 at its ends. The shaft is broken into two portions which in Fig. 3 are angularly displaced from their normal positions relative to each other about the shaft axis by 90 to show more clearly the structure of the rotor assembly. |iwo coil brackets 5l and 89, which may be in the form of channels, are secured to the shaft 83. Coils 9| and 93 are secured, respectively, to the brackets- 81 and 89 in any; suitable mannerfasfby cementing .the.coi1s.thereto, andare suitablyV insulated therefrom. Since these coils'are rotatable about'the .axis of theshaft 83, they may be termed movable coils. To avoid undue deiiection of the shaft in response to shock, a bumper disk ymay be carried by the shaft at a centrally disposed point.. This bumper disk is proportioned to have a small clearancewith respect to thev statory assembly I. Consequently, if the shaft tends to deflect appreciably, the bumper engages the adjacent stator assemblytoprevent excessive deection thereof.

Itwill be observed that the coil 9| has two terminal leads 91 which are attached, respectively; to conductor strips 99 and itil. The coil 93 h'asftwov terminal leads |il3 which a-re attached, respectively, to conductor strips |95 and it?. The vconductorvstrips form part of a terminal assembly |05 which` is employed to connect the coils 9i and' 93 to certain of the conductors 59. As illustrated in Figs. 1, 3 and fl, the terminal assembly |59 is located adjacent one end of the rotor assembly. Such a locationA is preferable to a location intermediate the magnetic structures 5 and l from the standpoint of accessibility; For the purpose of insulating the tcrminalassembly from the shaft 83, an insulating sleeve Hl may be positioned about the shaft. In addition, a plurality of spacers in the form of collars H3, H4, H5, H6, Hl and H8 areA positioned on the sleeve lH. The collars are employed for locating the conductor strips in predeterminad axialrand angular positions withwrespect to thel shaft 99.

Because of 'theextreme angular movement of the shaft 83 with respect to the stator assembly, the conductor strips must be extremely flexible and capable of permitting the required angular movement of the shaft. To prevent contact between the conductor strips, a plurality of insulating barriers H9 are provided. may bev formed of an insulating materia1 such as mica.

It is desirable that the terminal strips be spaced angularly about the shaft as well as axially thereof. This spacing is illustrated in. Fig. 4. The end of each of the conductor strips, when in a free condition, is positioned to lie adjacent a separate lug.` 32| which is mounted on the stator assembly. Each conductor strip which may be formed of a` suitable material, such as copper or brass, may be. soldered to its asso-- ciated lug |2|.

ln order to locate the conductor Vstrips accurately. the collars H3 to H8 are provided with ntertting male and female parts. Since these collars all may beA similar in constructionfa description of one of the collars H3, should suice. Referring to Figs. 7, 8 and 9, itwill be observed that the. collar H3 has a cylindrical neck |23 projectingffrom one end thereof. This neck has a key |25 extending therefrom in a radial direction with respect to the axis of the collar. The opposite end of the collar is provided with a circular recess |27 and a keyway |29 proportioned to receive snugly the neck |23 and key 425 of an adjacent collar.V To facilitate reception of the neck |23 and the key |25 in an adjacent collar, these parts may have bevelled edges as illustrated in Figs. 7 and 8.- By inspection of Fig. 7, it Will be observed that the key |25 and the keyway |29 on each collar are displacedfrom each other about the axis of the collar by an angle 6. Consequently, when afplurality: of co1- These barriers.

lars are nested, as shown in Fig. 3, each collar is displaced angularly with respect to an adjacent collar by the angle 0.

For positioning the collars with respect to the shaft 63, each collar may be provided with a keyway |3l, as illustrated in Figs. '1, 8 and 9. In order to distinguish the keyways from each other, the keyway |3| may have a height and width smaller than the corresponding height and width of the keyway |23. As shown in Fig. 3, the keyway l3| of one of the collars |l3 is positioned to receive a key |33 formed on the bracket 81. The angular relationship between the key |33 and the adjacent collar ||3 is clearly shown in Fig. 12. Consequently, all collars are accurately positioned both angularly and axially with respect to the shaft 83. Axial movement of the collars is prevented by a disk |35 secured to the shaft 83 which also serves to support a counterweight |31 for the pointer 4|. The collars may be formed conveniently by a molding operation from a suitable insulating material such as a phenolic resin. For receiving the terminal leads from the coils l and 93, the collars are provided with peripheral recesses |30 and |40.

The conductor strips all are of substantially similar construction and may be discussed with reference to Figs. and 11 which illustrate the conductor strip |01. The conductor strip |01 has its inner end connected to a holder |43 in the form of a sheet of electroconductive material. The holder |33 has a lug |45 bent at right angles thereto which is soldered to the inner end of the conductor strip. The holder |43 has an opening |41 formed therein for the purpose of receiving snugly the neck |23 and the key |25 of a collar. It will be observed that peripheral recesses |150 and |5| are provided in the holder for receiving the terminal leads of the coils 9| and 93. It will be observed further that the holder |33 has a terminal lead |53 projecting therefrom. This terminal lead is bent at right angles to the holder |43 along the line |55. The direction of the bend depends upon the position of the conductor strip with respect to the shaft 83 and will be discussed in greater detail below. For the specific conductor strip |01 illustrated in Fig. l1, the terminal lead |53 is bent downwardly.

The construction of the terminal assembly will be understood more fully from a consideration of Figs. 12 to i7, in conjunction with Fig. 3. As shown in Fig. 12, the collar |53 is positioned to receive the terminal leads 91 and |03. The terminal strip 00 has its holder |43 positioned over the neck |23 and key |25 of the collar I3. This positions the conductor strip 95, as shown in Fig. 13. Referring to Fig. 3, it will be observed that the lug |55 associated with the conductor strip 59 extends in a vertically upward direction, as viewed in Fig. 3, whereas the terminal lead |53 associated with the conductor strip 93 is bent downwardly to form one of the leads 01.

The conductor strip lill is associated with the collar ll in the same manner in which the conductor strip 33 is associated with the collar H3. It will be recalled, however, that the collar llll is displaced angularly about the shaft 83 with respect to the collar ll3 by the angle 0. Consequently, the conductor strip lill occupies the position illustrated in Fig. 14 when the conductor strip 99 occupies the position illustrated in Fig. 13. The terminal lead |53 of the holder associated with the conductor strip |0| is again bent downwardly to form the other of the two terminal leads 91. Theseterminal leads 91 have insulating tubing applied therearound as shown in Fig. 3.

The collars H5 and ||6 have only a barrier ||9 therebetween. This barrier has a central opening configured to receive snugly the neck |23 and key |25 of the collar ||5. By inspection of Fig. 15, it will be observed that the barrier ||9 also has openings |51 and |59 therein to provide passage for the various terminal leads. A similar barrier, as previously indicated, is positioned between each pair of collars.

The conductor strip |05 is positioned to receive the neck 23 and key of the collar IIB. This conductor strip and its holder are reversed with respect to the conductor strips 09 and |01 to position the free end of the strip |05 on the opposite side of the shaft 83. This means that the lug |45 associated with the conductor strip |05 extends downwardly as viewed in Fig. 3. The terminal lead |53 associated with the conductor strip |05 is bent downwardly to form one of the terminal leads |03.

The conductor strip |01 and its holder are associated with the collar l|1 in the same manner in which the conductor strip |05 and its holder are associated with the collar llB. However, inasmuch as the collars ||6 and ||1 are displaced from each other angularly by the angie 9, the free ends of the conductor strips |05 and lt'i are angularly spaced as illustrated in Figs. 16 and 1'1.

By adjusting the strips to be unstressed at the mid-scale position of the pointer the maximum deflection of each strip from its unstressed position corresponds to half the maximum arc of rotation of the rotor assembly. Since the strips associated with one of the movable coils unwind while the remaining strips wind, the possibility of unwound springs moving outside the barriers to establish an undesirable connection oi the movable coils is minimized.

The rotor assembly of Fig. 3 includes the pointer 4l and the damping disk 13 which are attached to a hub l6| mounted on the shaft. This hub also supports balance arms |63 having adjustable balance weights thereon and a lug |65 to which the inner end of the control spring 21 is attached.

The relationship between the rotor assembly and the magnetic structures 5 and 1 is illustrated in Fig. 4. The magnetic structure 1 includes a magnetic portion A having an annular magnetic core Al. This annular magnetic core is proportioned to pass through the coil 93 and has a channel A3 extending radially from the interior to the exterior of the annular core for the purpose of permitting passage of a side 0f the coil 83 therethrough. It may be noted that the annular magnetic core Al and the coil 93 are linked together in a manner analogous to the linking or" two links of a chain. The annular core Al has a magnetic member A5 projecting therefrom adjacent the channel A3 to connect the annular core Al to an outer magnetic element Ai. The annular core AI and the magnetic element A1 have adjacent surfaces which are spaced to denne an annular air gap A9 within which a side of the coil 93 is positioned for rotation. This annular air gap may be of sufficient length to permit angular rotation of the coil S3 about the axis of the shaft 83 for an angular distance of the order of 250. It will be observed that the annular core Al and the magnetic f member A are substantially inthe form :'of. a.. hook wherein the annular core Al 1s the hook section and the magnetic'member A5 is the shanksection. A xed coil AB surrounds the vmagnetic :memberAE and when energized produces a magnetic eld .in lthe annular air gap A8.

vBecause of the channel A3, the annular core Al for `the coil 93, is asymmetric with respect to the path of travel of the coil. Such asymmetry is undesirable because of the solenoid action resulting from currentflowing through the coil 93. This may be understood by assuming that theccoilAB is deenergized and that a current flows, inthe coil 93. Under these conditions, no torquershould be applied to the shaft 33 by the coil 93. However, because of the asymmetry of thev annular magnetic core, the coil 93 tends to move to a position wherein the reluctance of thel magnetic path associated therewith is a minimum.

In order to eliminate substantially this solenold action, the magnetic structure l includes a secondmagnetic portionvB which is similar to the magnetic portion A, but whichnis reversed with `respect tothe magnetic portion A about an'zaxisv perpendicular to the shaft S3 and parallel tothe magnetic member A5. Since the magnetic 4portionsprfl. and B are similar in construction, Vparts of the magnetic portion B will be designated `by the reference` character B followed by the numeral applied to the corresponding part of Ythe magneticportion A.

By Vinspection of Fig. 4, it will be observed that the asymmetries .of the magnetic portions A and B with respect to the path .of travel of the coil 93 are such as to produce a resultant magnetic structure which is substantially symmetric with respect to the path of travel of the coil. This is accomplished by positioning the channels A3 and B3 adjacent opposite ends of the path of travel ofther coil S3. -As a result of this construction, substantially no torque resulting from solenoid action is applied by the coilt to the shaft 83.

summarizing the discussion oi solenoid action, whencurrent passes through the coil 93 alone, the solenoid reaction between the magnetic portion Aand the coil 93 causes the coil to seek a position wherein the reluctance offered to magnetic flux produced by the current flowing inthe coil is a minimum. At the same time a solenoid reaction takes place between the magnetic portion B and the coilf. However, since the magnetic portions A and B are reversed with respect to each other,` thev torques or forces resulting from the two aforesaid solenoid reactions act on the coil 93 to a substantial extent in opposite directions and substantially compensate for each other.

1n order to permit the insertion of a preformed coil into-embracing relationship with the annular magnetic cores Ai and Bl, the magnetic portions-A and B are spaced axially along the shaft Sli-in any suitable manner for a distance suiiicientl to permit passage of a side of the coil 93 therebetween. `Preferably the spacer isv a magnetic structures which is similar to the magnetic portion Al except tor the omission of the annular magnetic core Ai. Although the magL netic portions A and Band the spacer S may be iormedof magnetically soft iron or steel of solid section, preferably they are laminated, as illustrated inlig; 4. Suitable shapes for the laminations are show-nmoreclearly'in Figs. 5 and 6. It will beobserved that the lamination employed for the` magnetic portion. A' is provided withv four holes AIB for receiving mounting bolts and additional holes AIS and All for receiving rivetslgto be employed in securing vthe laminations to each other. In aA similar manner, the lamination for the spacer is provided with holes Sl3 and SI5.

The required congurations and holes of the laminations may be formed readily by accurate punching operations.

Referring again to Fig. 4, the laminations in the magnetic portion A are'secured to each other by. means oi rivets AIS which pass through the holes All in the various laminations (shown in Fig. 5). in. a similar manner, the laminationsl in the magnetic portion B are attached to each other by rivets BIS. The magnetic portions A and B, together with the spacer S, then are firmly attached to each other by rivets SI1 which pass through the holes Al 5, SI5 and BIE in the various laminations.

In instruments of the type illustrated in Fig. 4, the spacing between the coil 93 and the magnetic structure l is extremelysmall. For this reasonif the instrument is employed in an installation subject l to excessive shock, precautionA should `be taken to prevent deflection of parts of the .magnetic structure into engagement with the coil 93. It will be observed that the annular core AI and the magnetic member A5 form essentially a cantilever structure, Even though rivets are employed for securing the laminations together, slight movements of the laminations with respect to each other may result from the applicationl of excessive shock to the instrument. This movement may suffice to bring one of the annular cores into engagement with the coil 93 and may result in damage to the coil. For this reason, it may be desirable to impregnate the laminations employed in an .instrument to be subjected to excessive shock with a suitable cement or varnish, such as phenolic resin varnish and, after riveting the laminations together, to bake the magnetic structure The baking operation converts the magnetic structure and varnish into the equivalent of a solid structure and substantially reduces .the deflection of portions thereof in response to excessive shock.

The magnetic structure 5 is similar in construction to the magnetic structure l. For reference purposes, however, the magnetic portions of the magnetic structure 5 are designated by the reference characters C and D and the fixed-coil for vthe magnetic structure 5 is designated by the reference character CD. The fixed coils AB and CD generally are of similar construction. Parts of the magnetic portions C and D corresponding to similar parts of the magnetic portion A are designated by the reference characters C or D Yfollowed by the` numerals employed in designating the corresponding parts of the magnetic portion A.

By inspection Vof Fig. 4, it will be observed that the magnetic structures 5 and 'l are displaced from each other angularly about the shaft 83 by TheY reason for this displacement may be understood by assuming initially that the magnetic-structures are similarly oriented with respect to the shaft. Under this assumed condition, the coils 9i and 93 would be disposed on the same side of the shaft 33. Since these coils represent. substantial portions of the total weight ofthe rotor assembly, a substantial counterweight would be required to balance the combined weight of the two coils. This would result in an undesirably heavy rotor assembly and would be accompanied by increased friction andbearingwear.

11 In addition, under the assumed condition, the xed coils AB and CD would be disposed ony the same side of the shaft 83. This would bring the xed coils into proximity to each other and magnetic interference between the two coils might result. To prevent such interference, a magnetic shield might be required between the two xed coils under the assumed condition.

By displacing the magnetic structures and 1 about the shaft 83, as illustrated in Fig. 4, the coils 9I and 93 are disposed on opposite sides of the shaft 83 and inherentlybalance each other. In addition, the xed coils AB and CD are disposed on opposite sides of the shaft 83. With this positioning of the fixed coils, it has been found that in most applications no shielding is required therebetween.

It is believed that the procedure for inserting the rotor assembly in the magnetic structures 5 and 1 now may be set forth. In assembling the instrument, the magnetic structures 5 and 1 are completed and attached to the base member 9 as shownv in Fig. 1. The 'rotor assembly 3 then is completed as illustrated in Fig. 3. Turning now to Fig. 4, to facilitate reference thereto the lower sides of the coils 9| and 93 will be designated, respectively, leading sides 9 IA and 93A, whereas the upper sides of these coils will be designated trailing sides SIB and 93B.

The complete rotor assembly is positioned on the axis of the annular magnetic cores and the leading side 93A of the coil 93 is positioned adjacent the channel C3 of the magnetic structure 5. The rotor assembly then is dropped to pass the leading side 93A through the channel C3 until it is stopped by the anular core DI. The rotor assembly 3 next is rotated in a clockwise direction (looking at the rotor assembly from the pointer end thereof) until the leading side 93A is positioned adjacent the channel in the annular magnetic core DI. The rotor assembly 3 thereupon is dropped to pass the leading side 93A through the channel in the annular magnetic core DI until the trailing side 93B of the coil 93 engages the annular maginetic core CI. The coil 93 now is in position to embrace the annular cores CI and In order to pass the coil 93 completely through the magnetic structure 5, the rotor assembly 3 is rotated in a counterclockwise direction to position the trailing side 93B of the coil 93 adjacent the channel C3. Consequently, the rotor assembly may be dropped until the trailing side 93B engages the annular magnetic core DI. Rotation of the rotor assembly in a clockwise direction carries the trailing side 93B through the space between the annular magnetic cores CI and DI until the trailing side 93B is adjacent the channel in the annular magnetic core BI. The rotor assembly now may be dropped until the coil 93B is completely between the annular magnetic structures 5-and 1. It will be understood that the spacing of the magnetic structures 5 and 1 axially along the axis of the shaft 83 is suicient to permit rotation of the coil 93 therebetween.

At this stage, the coil 93 is located between the magnetic structures 5 and 1, whereas the coil 9I is located above the magnetic structure 5. The rotor assembly 3 is rotated next to bring the leading side 93A of the coil 93 adjacent the channel A3. Such rotation simultaneously brings the leading side 9IA of the coil 9| adjacent the channel C3. Therefore, the rotor assembly may be dropped to carry the leading sides 9IA and 93A, respectively, through the channels C3 and A3 until these leading sides engage respectively the annular magnetic cores DI and BI. Following this step, the rotor assembly 3 is rotated in a clockwise direction to bring the leading sides 9IA and 93A, respectively adjacent the channels in the annular magnetic cores DI and BI. Finally, the rotor assembly 3 is dropped to pass the leading sides 9IA and 93A through the channels of the annular magnetic cores DI and BI until the trailing sides 9IB and 93B are stopped, respectively, by the annular magnetic cores CI and AI. The coil 9| now is in position to embrace both of the annular magnetic cores CI and DI, whereas the coil 93 is in position to embrace both of the annular magnetic cores AI and BI. Therefore, the bridge plate I9 (Fig. 1) may be attached to the bearing support I I and the bearing screws I1 and 2| may be adjusted to position the shaft 83 for rotation with respect to its stator assembly.

As previously explained, the conductor strips 99, IDI, I and |91 have their ends accurately positioned adjacent their associated lugs I2I. Therefore, after installation of the rotor assembly, the ends of the conductor strips may be soldered to their lugs I2I.

By reversing the above procedure, the rotor assembly 3 may be removed from the magnetic structures 5 and 1 for servicing or replacement. It should be noted that the convenient assembly and disassembly of the rotor assembly with respect to the stator assembly is achieved without introducing errors resulting from the solenoid action previously discussed and without necessitating separation of the magnetic structures into a plurality of parts. The one-piece construction of the laminations is particularly desirable for instruments of the type herein discussed for the reason that extremely accurate angular air gaps in the magnetic structures 5 and 1 are required: This requirement may be understood by assuming that with the parts in the position illustrated in Fig. 4, the pointer il indicates a value of l0 watts. Let it be assumed further that the annular air gap in the magnetic structure 5 is not uniform and that the coil 9I is positioned in the portion of the air gap having minimum length. Let it be assumed further that the annular air gap in the magnetic structure 1 is not uniform, and that the coil 93 is positioned in the portion of the air gap having maximum length.

If the conditions of energization of the instrument are such that the coils AB and 93 are deenergized and the coils 9I and CD are energized with an energization corresponding to l0 watts in the associated electrical circuit, the coil 9| being positioned in a portion of its annular air gap having low magnetic reluctance produces an excessive torque and rotates the pointer 4I to indicate a value in excess of 10 watts. Let it be assumed that the energization of the units is reversed and that the coils 9| and CD are deenergizedl If the coils AB and 93 are energized by currents corresponding to a value of power of l0 watts in the associated electrical circuit, the coil 93 being in a portion of its air gap of maximum reluctance produces a low torque and advances the pointer 4I to indicate a value of power less than l0 watts. If the energization intended to indicate l0 watts of power is divided between the two units in different ratios, different values of power are indicated by the pointer 4I. For this reason, observation of the pointer il fails to indicate accurately the power of an associated electrical circuit. Since the errors vary in accordance with the distribution of the energization of the two encens? i3 units/it is; impossible" to 1 eliminate thererrorszby calibration .of Vthe .instrument scale. For these andother, reasons, it is desirable t construct the magnetic structures 5 and 'l of unitary laminations: having accurate air gaps therein.

VReferring again to Fig. l, it will be observed that an .annular bumper .plate ill is attached vto the stator .asembly to assist inlocating the stator assembly with respect to the shell 39. As shown in Figs, liland-` 20, this bumper plate also may supportan insulating block i773 on which the lugs lili aremounted.' The lugs, in turn, are connected throughfthe conductorsV 59 to appropriate terminalscrews 51er. the base member 9 (Fig. l).

.Eachsof the magnetic structurest and 'thas several: aligned openings .extendingthrough all laminations therein. See, for example, the openings AI'S and'Sli of Figs. 5 ando. A structure may lbe;l associated with each set of these aligned openings: for securing the magnetic structures to the base plate S. suitable structure for attachingrthe stator ,assembly to the basev member e is illustrated in Fig, 22. IThe magnetic-structures V5 and 'lareV provided with insulating sleeves il@ whichpass through the openings in the magnetic structures. For example, in the magnetic structure l, as shown in Fig. 22, the insulating sleeve llrS passes through the vcontiu'iuous opening formed by the holes A!3,.Si3 and BIS punched in thevarious laminations. At each end of each insulating sleeve ile, an insulating washer lili is; located with its yaxis aligned with the axis of t-heinsulating sleeve.

To'positiong the magnetic structure i .with respect to thefbase` t, a spacer i te is associated with eachof; the. insulating sleeves il@ in the magnetic structure l. `One of these spacers IBB is shown in'FigxZZ, The spacer 83 may-be inthe form of 'ei-hexagonal Inetallicmember having one end positioned against the base member -2 and its oposite'end' positioned in engagement with one of the insulating Washers lill. Each of the spacers 83 has two studs M5 and i3? projecting from its-ends. The stud i8? passes through the base member 9 and is securely attached thereto in a suitablerfmanner as by means -o'a nut 89. The shell-.zmay have ears Ela, projecting from the ange 5l through which the studs i3? project. Each earis secured by a nut l, a lock Washer itl :and a reeniorcing plate L52 to one or the studs. ltshould be noted that the shell il vand the' magnetic structures are all attached to the studsi'l. This substantially relieves the base member from stress. The shell i9 is suicently rigid tc'provide-support for theY magnetic structures. ln a similar manner four studs liii (Fig. 21) are provided for the'V magnetic structure l.

Each stud iSFa passes through its associatedv insulating sleeve il@ and insulating washers ii and through a boss ist formed on theplate i3. iheend of each stud it is in threaded engagement with a spacer ist whichserves tosecure the.

plate i' 3 and thev magnetic structure l' to the base member fl, in la somewhat similar manner, the spaoer'i't has a stud le? projecting therefrom through the associated insulating sleeve H9 and insulating Washers of the ymagnetic structure 5. A'nut E9s at the end of the stud is? secures the magnetic s ucture 5 to the spacer 25 and therethrough to thebase member e. it should be observed that with the specific mounting illustrated in Fig. 22,.al1 of the insulating members are in compression. Each of the studs lill also projects through the` bumper plate l'il. A nut Ztl and lockz'washer -are associated with each of the 1.4 studs |197 for thepurpose of securing thebumper plate Ill thereto.

As previously explained, the measuring instrumentillustrated in Fig,l 1 has. two separate singie-phase units. The .movable coils 9i and 93 cithe two units are attached to a common shaft. This instrument is suitable for measuring functions of electrical quantities present in a threewire or a polyphase electrical circuit. lf a singlephase measuring instrument is desired, only one o the units, such as that including the magnetic structure E and the coil 9i, may be employed. Such ameasuring instrument .is illustrated in Fig. 23, wherein parts similar to those of Fig. 'l are represented by the saine reference characters.. twill be observed that the coil Qi and the damping dislr i3 are mounted on a shaft Et which is somewhat shorter than the shaft 83 of Fig; l. The shaitl is rotatably supported in the bearing screws il .and 2 l. A support 227i corresponds to the support i l or" Fig. l. The casing, dial andA pointer assemblies of the instrument illustrated in Fig-23 may be similar to the correspending elements of Figi. For this reason, a description of the casing and other similar parts otF-ig. 23 is believed unnecessary.

Since theinstrument of Fig.V 23 has only one movable coil Si, a countervveight 2M is illustrated therefor.' Also the pointer di is positioned on the side of the shaft opposite the coil to balance part of the'weight of the coil. It will be noted that only the two conductor strips 99 and lill and two lugs tt are required for the rotor assembly of Fig. 23.

In assembling the instrument illustrated in Fig. 23. the coil 9i is threaded into embracing relationship withthe annular cores of the magnetic structure vE; -in the same manner discussed with reference to Fig. 4. After the `coil 9! is positioned'to embrace the annular cores, the. shaft is centeredfby means of the bearing screws i'd and 2l. Since the instrument of Fig. 23 comprises, -in eiect, one of the units of the instrument of 1, the description `of the latter instrument applies-in substantial part to the instrument of in connecting the measuring instruments of Figs. l and 23 to an electrical circuit, some compensaticn may be required to correct the phase displacements between magnetic fluxes in the magnetic structures produced because of the hysteresis losses in the magnetic structures 5 and l. Suitable'connections for one of the units are illustra-ted inFig, 24. In Fig. 2e, the xed and movable coils of one of the units are `associated with-an electrical circuit having the conductors Li `and L2. energization in accordance with the Voltage of the circuit, whereas'the other coil is connected for enei'gizationin laccordance:with current flowing in the circuit. inni-ost cases.` the movable c-oil el is connected for energization in accordance with voltage Whereas the Xed coil CD is connected for energization accordance with current. lt will be observed that the movable coil is connected across the conductors L! and L2 through a multiplier resistor having two sections till and 25,3. A capacitor is connected across the coil tl and one section titi of the resistor for the purpose oi compensating the unit .for the aforesaid phase displacement errors. Such compensation is well understood in the art. When a .polyphase measuring instrument similar to that shown in Fig, 1 is employed, it will be understood that compensa- 'Oneof the coils is connected for tion may be required for each of the units in the polyphase instrument.

Certain subject matter herein disclosed is disclosed and claimed in our copending application, Serial No. 757,260, filed June 26, 1947.

Although the invention has been discussed with reference to certain specic embodiments thereof, numerous modications are possible. The appended claims are drafted to cover all modications falling within the spirit and scope of the invention.

We claim as our invention:

1. In an electromagnetic device, a coil, a magnetic structure having an air gap, winding means associated with the magnetic structure for producing a magnetic ield in the air gap, means mounting said coil with a side in the air gap for movement relative to said magnetic structure over a predetermined travel, said magnetic structure comprising a first magnetic portion defining a path for magnetic flux produced by electrical current flowing through said coil throughout said travel, said magnetic portion providing a rst substantial magnetic solenoid force in response to said current acting between said magnetic portion and said coil, a second magnetic portion dening a path f-or magnetic flux produced by electrical current flowing through said coil, said second magnetic portion providing a second substantial magnetic solenoid force in response to current in said coil acting between said second magnetic portion and said coil throughout said travel, and means mounting said magnetic portions to direct said forces in opposition to each other, whereby movement of said coil is substantially unaffected by said forces.

2. In an electromagnetic device, a pair of annular magnetic cores, means supporting said magnetic cores axially spaced and in substantial alignment on a common axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis, and a coil linked with both of said magnetic cores.

3. In an electromagnetic device, a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, a magnetic member extending from each of said magnetic cores in substantially the same radial direction relative to said axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis, to position said channels adjacent, but on opposite sides of, said magnetic members, and coil means linked with said magnetic cores, said magnetic cores being spaced axially along said axis by a distance suicient to permit movement of a side of said coil means therebetween.

4. In an electromagnetic device, a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, a magnetic member extending from each of said magnetic cores substantially in a common radial direction relative to said axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis to position said channels adjacent but on opposite .rbers and said magnetic element dening a magnetic path for directing magnetic iiux into said air gap, coil means associated with said magnetic path for producing, when energized, magnetic flux in said air gap, a coil linked with both of said magnetic cores, said magnetic cores being spaced axially of said axis by a distance suiiicient to permit movement of a side of said coil therebetween, said coil being proportioned for removal from said magnetic core by successive passage of a side thereof through one of said channels, rotation of said side between said magnetic cores into alignment with the other of said channels and passage of said side through said last-named channel, and means mounting said coil for rotation relative to said magnetic cores in a path wherein a portion of said coil moves through said air gap.

5. In an electromagnetic device, a pair of units; each of said units comprising a magnetic body having an inner pole piece and an outer pole piece spaced to denne an annular air gap, stationary coil means associated with said magnetic body for producing, when energized, a magnetic rleld in said air gap, and a coil having a side positioned in said air gap for movement therethrough about a predetermined axis; means mounting said units with the axes of said coils in alignment, said units being positioned to space the stationary coil means of said units angularly about the common axes of said coils, whereby interference between said coil means is minimized, and means mounting said coils for rotation as a single assembly relative to the associated magnetic bodies.

6. In an electromagnetic device, a pair of units; each of said units comprising a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a com mon axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis, and a coil linked with both of said magnetic cores; means mounting said units with the axes thereof substantially in alignment, said magnetic cores being spaced axially along said axis to permit movement of a side of said coil through said channels and through the space between the magnetic cores, and means connecting the coils of said units for rotation about their common axis as a single assembly relative to said magnetic cores, said units being angularly displaced approximately from each other about their common axis, and said units being spaced axially of said common axis by a distance suicient to permit substantial rotation of one of said coils about said common axis when said last-named coil is positioned between said units.

7. In an electromagnetic device, a pair of units; each of said units comprising a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, a magnetic member extending from each of said magnetic cores in substantially the same radial direction relative to said axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis, to position said channels adjacent, but on opposite sides of, said magamaca? netlc; member, and coil meanslinked. with said magnetic cores; means mounting. saidunits with the axes thereof substantially in alignment; said units being angularly spaced about their common axis to position the magnetic membersl of the units on opposite sides of said common axis, and means mounting the coil means of both units for rotation as a single assembly about said common axis.

8. In an electromagnetic device, a pairY of units; each of said units comprising a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, a magnetic member extending from each of said magnetic cores in substantially the same radial direction relative to said axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis, to position said channels adjacent, but on opposite sides of, said magnetic member, irst coil means linked with said magnetic cores, and second coil means surrounding said magnetic members for directing magnetic ux into said magnetic cores when said second coil means is energized; means mounting said units with the axes thereof substantially in alignment, said units being angularly spaced about their common axis to position the magnetic members of the units on opposite sides of said common axis, and means mounting the first coil means of both units for rotation as a single assembly about said common axis.

9. In an electromagnetic device, a pair of units; each of said units comprising a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, a magnetic member extending from each of said magnetic cores substantially in a common radial direction relative to said axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior oi each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis to position said channels adjacent but on opposite sides of said magnetic members, a magnetic element surrounding said magnetic cores but spaced therefrom to dene as arcuate air gap therebetween, said magnetic cores, said magnetic members and said magnetic element deiining a magnetic path for directing magnetic ilux into said air gap, coil means associated with said magnetic path for producing, when energized, magnetic flux in said air gap, a coil linked with both of said magnetic cores, said magnetic cores being spaced axially of said axis by a distance suicient to permit movement of a side of said coil therebetween, said coil being proportioned for removal from said magnetic core by successive passage oi a side thereof through one of said channels, rotation of said side between said magnetic cores into alignment with the other of said channels and passage of said side through said last-named channel, said coil being disposed for rotation about said common axis in a path wherein a portion of said coil moves through said air gap; means mounting said units with their axes substantially in alignment, and means mounting the coils of said units for movement as a single assembly about their common axis relative to said magnetic cores, said units being displaced angularly about their common axis by substantially 180, and said units being spaced axially along their common 1'8 a distance sufficient: to.- permit substantial; rotation ofloneof said' coils when positioned betweensaid units. to permit alignment ci said coils. with; the channels, of: their respective units during assembly ci the device.

10. In an electromagnetic device, a. magnetic structure dening ak magnetic path including: an air.- gap, said magnetic structure including an Iam.- inated; cantilever'magnetic4 core, a coil. surround:- ing said; magnetic' core andjslightly spaced therefrom taper-mit relative movement therebetween, said coil. having aside positionedv in said air gap, means mounting said', coil for' movement relative to said magnetic. core in a path wherein` said side moves: through said air gap, adhesive bondingmeans firmly uniting the laminations of said magnetic core for restricting de'ection of' the free end of said cantilever magnetic core with respect` to the fixed/'end of said core, and means associated with said magnetic structure for producing magnetic ux in said air gap.

1l. Ih an electromagnetic device, a pair ofsimilar magnetic structures, each of said magnetic structures comprising a hook-shaped magnetic core having a hook section and having a shank section projecting from said hook section, each of said magnetic structures also comprising a magnetic member surrounding', but spaced from, a substantial portion or the associated hook section to form therewith an arcuate air gap, said hook section, shank section andV magnetic member of each of said magnetic structures dening a magneticY path for directing magnetic flux through the associated air gap, and means mounting' said magnetic cores with their hook sections extending around a common axis and with their' shank sections all' extending away-from said axis'irr sub*- stantially the same radial direction, one of said magnetic cores being'reversed relative to the other of the magnetic cores abouty an axis parallei to said radial direction, a spacer intermediate said magnetic structuresy fory spacingl said magnetic structures axially along said first-named axis, said spacer comprising a magnetic body having facesA engaging said magnetic' members and ter'- minatirrg short ofthe hook sections of said maginetic cores, whereby said hook sections have an air space therebetween.

12. In an electromagnetic measuring instrument, a pair of measuring units; each of said units comprising a magnetic structure having an air gap, and a coil having a portion positioned for rotation through said air gap, a .portion of said magnetic structure extending through said l coil in a predetermined operative position of said coil relative to said magnetic structure, said coil being movable at least partly in an axial direction from said operative position to a position external to said magnetic structure; shaft means mounting the coils for rotation as a single entity relative to the respective magnetic structures, and terminal means for both of said coils positioned on the shaft means adjacent a rst end of said shaft means external to said magnetic structures.

13. In an electromagnetic device, a pair of units, each of said units including a plurality of magnetic structures, each of said magnetic structures comprising a, hook-shaped ma-gnetic core having a hook section and havinga shank section projecting from said hook section, and means mounting said magnetic cores with their hook sections extending around a common axis and with their shank sections all extending away from said axis in substantially the same radial 'reversed relative to the remainder of the magnetic cores about an axis parallel to said radial direction, and means mounting said units in spaced relationship with their common axes in alignment.

14. In an electromagnetic device, a pair of units, each of said units including a plurality of magnetic structures, each of said magnetic structures comprising a hook-shaped magnetic core having a hook section and having a shank section projecting from said hook section, and means mounting said magnetic cores with their hook sections extending around a common axis and with their shank sections all extending away from said axis in substantially the same radial direction, certain of said magnetic cores being reversed relative to the remainder of the magnetic cores about an axis parallel to said radial direction, and means mounting said units in spaced relationship with their common axes in alignment, said units being spaced `angularly about the line of their common axes by substantially 180, and one of said units being inverted with respect to the other of said units.

15. In an electromagnetic device, a pair of units; each of said units c-omprising a pair of annular magnetic cores, means supporting said magnetic cores in substantial alignment on a common axis, each of said magnetic cores having a channel therein extending radially relative to said axis from the interior to the exterior of each of said magnetic cores, the channels in said magnetic cores being spaced angularly about said axis,` and a coil linked with both of said magnetic cores, said magneticA cores having a space therebetween sufficient to permit movement of a V side of said coil between said magnetic cores, said coil being proportioned for movement through the passage formed by said channels and said space from a position external to said magnetic cores to a position wherein said coil links said magnetic cores; means mounting said units with the axes thereof substantially in alignment, and

means connecting the coils of said units for movel ment as a single assembly relative toV said magnetic cores, said units having a space therebe- Number tween which with said passages forms a resultant passage through which one of said coils may be moved from a position linking a rst pair of said magnetic cores to a position linking a second pair of said magnetic cores.

16. In an electromagnetic device, a pair of similar magnetic structures, each of said magnetic structures comprising a hook-shaped magnetic core having a hook section and having a shank section projecting from said hook section, each of said magnetic structures also comprising a magnetic member connected to the shank section and surrounding, but spaced from, a substantial portion of the associated hook section to form therewith an arcuate air gap, a coil having a coil side disposed in the air gaps for movement therethrough, said hook section, shank section and magnetic member of each of said magnetic structures dening a magnetic path for Adirecting magnetic ux through the associated air gap, and means mounting said magnetic cores with` their hook sections extending around a common axis, one of said magnetic cores being reversed relative to the other of the magnetic cores about an axis parallel to said radial direction, said magnetic cores being spaced axially along said first-named axis to complete a passage extending through the magnetic cores to permit insertion and removal of the coil therethrough relative to the magnetic structures. DOUGLASS A. YOUNG. LAWRENCE J. LUNAS. BERNARD E. LENEHAN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Name Date Faus Mar. 1, 1932 Simpson Mar. 14, 1933 Faus July 11, 1933 Graneld Mar. 27, 1934 Corson Oct. 15, 1940 Lederer Nov. 12, 1940 Putman Apr. 6, 1943 

